The invention relates to improvements in shock absorbers with variable damping characteristics, especially to shock absorbers which can be utilized in motor vehicles. More particularly, the invention relates to improvements in shock absorbers of the type wherein the internal space of at least one cylinder is divided into two cylinder chambers by a piston which is sealingly and reciprocally received in the cylinder and is connected with one end of a piston rod. The piston rod extends from the cylinder and is connectable to one part of a motor vehicle. Another part of the vehicle (which is movable relative to the one part or vice versa) is connected with the cylinder, and the purpose of the shock absorber is to damp relative movements of the two parts. The chambers of the cylinder are filled with at least one damping fluid (such as oil), and the piston defines a passage for the flow of damping fluid from one of the chambers into the other chamber when the piston moves in one direction or from the other chamber into the one chamber when the piston moves in the opposite direction.
It is already known to provide a shock absorber of the above outlined character with electrically operated means for regulating the rate of flow of damping fluid between the two cylinder chambers in order to regulate the damping action of the shock absorber. Reference may be had, for example, to commonly owned U.S. Pat. No. 4,765,445 to Komossa et al. which discloses a shock absorber with a variable damping characteristic wherein the piston has one or more passages for the flow of damping fluid between the cylinder chambers and the piston is further provided with several bypass channels which extend between the two cylinder chambers. Discrete electrically operated means are provided for individually regulating the flow of damping fluid through the bypass channels.
A shock absorber with one or more bypass channels in the piston is also disclosed in commonly owned copending patent application Ser. No. 428,458, filed Oct. 30, 1989, which is a continuation of Ser. No. 254,191 filed Oct. 5, 1988, now abandoned.